Cable Suspension Arrangement for a Wind Energy Converter, Corresponding Mounting Method and Corresponding Spacer Plate
The present invention relates to a cable suspension arrangement for a wind energy converter, to a corresponding mounting method and to a corresponding spacer plate.
A wind energy converter is a rotating machine which converts the kinetic energy in wind into electricity and feeds the electricity into the electrical grid.
A wind energy converter generally includes a nacelle disposed on a tower. The nacelle (also called gondola) includes a rotor head equipped with blades and a main shaft connected to the rotor head so as to integrally rotate with the rotor head. Moreover, the nacelle can rotate around a vertical axis so as to actively or passively follow the wind direction.
A first type of nacelle further includes a gear box connected to the main shaft that rotates upon receiving the wind power supplied to the blades, and a generator driven by an output shaft from the gear box. According to the wind energy converter having this structure, the rotor head equipped with the blades converts wind power into a rotational force, and the main shaft rotates to generate a first rotational speed. The first rotational speed is increased via the gear box connected to the main shaft, and a corresponding second larger rotational speed is transmitted to the rotor of the generator. A second type of nacelle without gear box uses direct drive turbines with DC generators. Special high power electronics convert from DC to AC electricity.
The electrical energy produced by the generator will be transferred by cables which are installed in the tower. Since the nacelle must always turn the rotor into the wind direction and the desired range of yawing is two revolutions clockwise and two revolutions counter clockwise, the power cabling will be highly stressed and there is the potential risk of damage.
FIG. 5 is a side view showing an example of the conventional overall structure of a wind energy converter.
As shown in FIG. 5, a wind energy converter 1 includes a tower 2 disposed on a foundation 6, a nacelle 3 provided on the upper end of the tower 2 which is rotatable around a substantially vertical axis B, and a rotor head 4 provided on the nacelle 3 including a hub for fixing rotor blades 5 which rotor head 4 is rotatable around a substantially horizontal axis A.
A plurality of blades 5 is attached to the rotor head 4 so as to be radially disposed around the rotation axis A. Thereby, wind power supplied to the blades 5 from the direction of the variable rotation axis A of the rotor head 4 is converted into mechanical power for rotating the rotor head 4 around the rotation axis.
FIG. 6 is an example of a conventional cable suspension arrangement of the wind energy converter of FIG. 5.
As depicted in FIG. 6, a nacelle 3 (only part of the contour of a main frame is shown in FIG. 6) is supported on bearings 25 which are located on a platform 20 on top of the tower 2. Reference signs L1, L2, L3 denote a first, second and third cable, which connect a not-shown generator in the nacelle 3 with the electrical grid. For the sake of simplicity, only three cables L1, L2, L3 are shown here; however, normally there are between 15 and 50 cables which have to be bundled and let down from the top of the tower 2 to the bottom of the tower 2.
Since the cables L1, L2, L3 typically have a cross-section of 150 mm2 or more and have a length between 10 and 15 m, it is necessary to implement a suspension means for stress relief, cable guide means and cable spacing means.
Conventionally, the suspension means is realized as a cable stocking arrangement as schematically depicted as H1, H2, H3 in FIG. 6. Specifically, each cable L1, L2, L3 wears a cable stocking which is hooked to a part of the nacelle 3 so as to be rotatable together with the nacelle 3.
Moreover, there is spacer plate 31 having through-hole 61, and spacer plate 32 having through-hole 71, where the cables L1, L2, L3 are led through and either clamped therein or fixed thereto by cable ties. The spacer plates 31, 32 are fixed to the tower 2 wall by a respective fixing means 312, 322.
If the nacelle 3 rotates, the cables L1, L2, L3 are drawn upwards.
Below the second spacer plate 32 the cables L1, L2, L3 are guided to the sidewall of the tower 2 via a so-called cable loop L and via a supporting cylinder 40. The supporting cylinder 40 is fixed at the sidewall of the tower 2 by a corresponding fixing means 41 denoted by dashed lines in FIG. 6.
Moreover, there is a fixture 50 attached to the sidewall of the tower 2 which fixes the cables L1, L2, L3 in corresponding through-holes 51, 52, 53, e.g. by a clamping mechanism or by cable ties.
Upon rotation of the nacelle 3, the cable loop L can move upwards and downwards along the direction of the arrow P3 so as to vary the free length of the cables L1, L2, L3.
It should be noted that the length of the cable loop L (typically 2.5 m) is arranged such that the twist and upward and downward movement of each cable L1, L2 and L3 can be absorbed.
Since the fixture 50 is not pivotable and there is the supporting cylinder 40, a transfer of the cable twist to the tower 2 sidewall can be prevented.
Upon turning of the nacelle 3 up to two revolutions, the power cabling and suspension parts will be highly stressed. While turning, cable ties can damage the casing of the cables. The inner surface of the spacer plates 31, 32 can also damage the casing of the cables. Moreover, there are heat dissipation problems in conjunction with the cables L1, L2, L3 because they are densely packed at the spacer plates 31, 32. In other words, this arrangement impedes sufficient heat dissipation.
Finally, the installation of the cabling and guiding of the cables is complex. After the nacelle 3 is connected to the top of the tower 2, all tower cables have to be installed into the spacer plates and fixtures by hand, and in the case of the use of cable ties, each individual cable tie has to be fixed manually.
Thus, a worker has to climb up and down several times in order to install the cabling in the correct way. For the crimping of the cables to the tower wall, the worker needs heavy tools. In order to uninstall the nacelle to change the gear box, the worker has to cut the cabling and then has to re-install the cabling after replacement of the nacelle 3. In this case, the worker needs heavy tools and to climb up and down the tower several times.
U.S. Pat. No. 6,713,891 B2 discloses a wind turbine including a cable suspension and cable spacing devices for maintaining a constant distance between the cables hanging down through the tower. The stable spacing devices are suspended down along a wire or a rope. The cable spacing devices have a polygonal or circular circumference and are provided with slots that extend from the circumference towards the centre. The centre is provided with a hole through which the wire or rope on which the cable spacing device is suspended can run. The cables are clamped at the inner ends of the slots.